Great Northern / LNER 4-6-2 Locomotives in Great_Britain

Class A1 (Locobase 1065)

Data from Edward Cecil Poultney, British Express Locomotive Development (London: George Allen and Unwin, 1952), p. 129-133. See also "Three-Cylinder 4-6-2 Locomotive, Great Northern Railway", Railway Engineer, Volume 43, No 5 (May 1922), pp. 176-180; and Richard Marsden, "The LNER A1 and A3 Gresley Pacifics" in his LNER Encyclopedia at [], last accessed 1 February 2021.

Designed by Nigel Gresley, this locomotive is said by analysts on both sides of the ocean to have been influenced by the Pennsylvania Railroad's K4s Pacifics of 1914. The Great Northern design, however, put only two-thirds as much weight on the drivers as did the K4.

Fitted with three sets of Walschaert gear, the third, middle gear being driven by links from the other two; steam was admitted by 8" (203 mm) piston valves. All three cylinders drove the second axle. Glover (1967) claimED that the boiler was a relatively new design, consisting of a first parallel course of 77" diameter and a forward course that was coned around a central axis. Moreover, the firebox lines sloped in in and down front to back ,which improved visibility. In the front of the firebox, the throat plate had a continuous forward slope from the base to the boiler centerline, which gave the firebox a combustion chamber.

In comparing this locomotive to Raven's North Eastern design, Glover contends that the A1 "provides an outstanding example of the application of fresh thought to the new problem." But Marsden offered an example of fresh thought resulting in standing pat. 1925 test showed any improvements in steaming from a new Type E superheater were "small and uneconomic". The Robinson " concentrated the superheater tubes where they would be most effective. Hence the extra tube surface area in the new superheater, had to be in less effective areas of the boiler."

Troublesome at first, but when well-maintained, ran very fast, especially after the 1925 exchange of locomotives between the LNER and the Great Western. During those trials, the GWR's Castle-class 4-6-0 showed itself the equal of the A1 in every respect even though it was smaller and lighter. Gresley modified the valve train to lengthen full-gear travel, reset lap to 1 5/8" (41.275 mm) on the outside cylinders and 1 11/16" (42.86 mm) on the inside, lead to 1/8" (3.175 mm), and limit full-gear cut-off to 65% of stroke. Performance with the new valve setting, says Cecil Poultney, "...was vastly improved, tho coal consumption being much reduced." In fact, to run a heavy train from Doncaster to London now required a full ton less than before.

This design later evolved into the record-setting A4s (1066).

Richard HN Hardy (see Locobase 2314 for a discussion of this photographer and his extensive collection of LNER images; see [], accessed 8 May 2006) offered this succinct appraisal of the design: "Those old A1s could time the heavy trains with their big cylinders even when down to 140 psi [9.65 bar] or so whilst an A3 or, even more, and A4 would be struggling if short of steam."

Class A1/1 (Locobase 20835)

Data from Type A-1/1 diagram supplied by Jonathan VanAken, along with a detailed breakout of specifications, in a 31 January 2021 email. See also Edward Cecil Poultney, British Express Locomotive Development 1896-1948 (London: George Allen and Unwin, Ltd, 1952), p. 170; and Richard Marsden, "The Thompson A1/1 Pacific" in his LNER Encyclopedia website at [], last accessed 1 February 2021. (Many thanks to Jonathan VanAken for putting together the data and source material.)

Nigel Gresley's A1 class (Locobase 1065) entered service on the Great Northern in 1922. In 1944, Chief Mechanical Engineer Edward Thompson decided to build one new engine based on the A1, but using the A4 boiler. This was to be the prototype for a class of new Pacifics that remedied what Thompson saw as defects in the Gresley A4s.

Few locomotive projects have attracted as many boos as this one. Marsden summarizes by citing the principal offense: "A1 (by then reclassified A10) No. 4470 Great Northern was selected for rebuilding. It is unfortunate that Great Northern (the very first Gresley Pacific) was chosen for this rebuilding, rather than being selected for future preservation. There has been much debate on the reason for this choice. Some state it as bad luck, whilst others clearly blame Thompson for letting his personal feelings towards Gresley to cloud his judgement. It is known that the Chief Draughtsman and a number of high up officials within the LNER unsuccessfully tried to deter Thompson from rebuilding this engine ."

A 29 August 2019 post by Neil Dimmer--" Edward Thompson pacifics of the LNER : A1/1 60113 Great Northern"-- to main@UK-Rail.groups, found at [],0,0,0::recentpostdate%2Fsticky,,,20,2,0,33071905 quotes two well-known authors: "O. S. Nock describes it as 'the most disappointing and tactless act in his short and stormy career as CME,'and [Cecil J] Allen stated 'he turned it into a machine of such hideous appearance as might well have made its designer turn in his grave.'"

Notwithstanding the widespread dissent, Thompson converted the 4470 and his "modifications" doubtless fueled resentment as he scrapped most of the original in favor of building new, longer frames and fitting a new larger boiler. He moved the middle cylinder out of line with the two outside cylinders, rejecting the option of moving it forward in favor of positioning it farther back. All three used individual sets of Walschaert gear actuating 10" (254 mm) piston valves. The longer wheelbase caused the engine to yaw to a considerable degree.

Thompson's retirement in 1946 meant that rebuilding the sixteen remaining A1s to this standard were abandoned by the new CME Arthur Peppercorn who undertook a rebuild program of his own (Locobase 1067).